The present invention relates to fluid spray guns. More particularly, the invention provides a modular design for a fluid spray gun which permits the gun to be configured to operate with a selectable spray process such as airless, air assisted airless, air spray and HVLP, with significantly reduced inventory requirements and minimal parts changes and assembly labor. The gun is provided in an electrostatic and non-electrostatic version.
Fluid spray guns are generally known and are commonly used to spray a wide variety of fluids on any number of different types of articles. Spray guns can be used, for example, to spray fluids such as paint, lacquer, cleansers, sealants and so forth. Fluid spray guns may be hand operated or automatic depending on the specific application system requirements.
Fluid spray technology includes a number of spraying modes or spraying processes for applying a fluid to an object. A fundamental characteristic of all spray processes is that the fluid is atomized before it is applied to the object being sprayed. The spray processes differ in the manner by which the fluid is atomized, with the goal being a finely atomized spray that is released from the spray gun in a well defined spray pattern. The spray pattern can be shaped by the selected atomization process as well as by the design of the spray nozzle used with the spray gun. Thus, different spray technologies not only use different atomization processes but also may use different nozzle designs.
A familiar spray process is air spraying which utilizes pressurized air to atomize the fluid at the region of the spray nozzle outlet. Air spray guns thus tend to be operated at lower fluid pressures such that in the absence of an atomizing air supply the fluid simply runs out the nozzle as a small stream. The atomizing air is usually on the order of 10 to 100 psi. Therefore, the spray gun must be able to withstand such air pressures.
In some cases it is desirable or required to operate air spray guns at a reduced air pressure. Using lower atomizing air pressure may in some cases reduce fluid bounce back from the object being sprayed and thus increase transfer efficiency. Such spraying systems are generally referred to as using a high volume low pressure xe2x80x9cHVLPxe2x80x9d hereinafter) spray process. In a typical HVLP process, the air pressure at the nozzle is kept to less than 10 psi but the spray nozzle is designed to increase the volume of air directed at the fluid spray. Thus, HVLP is a variation of air spray technology but utilizes a different spray nozzle design. Spray guns for HVLP operation also require a mechanism by which the air pressure at the nozzle can be tested for compliance with the under 10 psi requirement.
In both air spray and HVLP spray processes, the atomization air may not fully atomize the fluid or may produce an undesired spray pattern. Air spray guns therefore also utilize horn air. Horn air is a second source of pressurized air that is applied to an outer region of the atomized fluid spray pattern to shape the spray pattern and also to improve atomization of the fluid in the outer regions of the spray pattern.
Another fluid spray process is airless spraying. As suggested by the name, an airless spray process does not use high pressure air for primary atomization of the fluid. Rather, the fluid is supplied under high pressure to a small orifice in the spray nozzle. The kinetic energy applied to the liquid as it passes through the orifice breaks apart the fluid stream into a finely atomized spray, much like a garden hose nozzle produces a spray of water. In airless spray apparatus the fluid may be pressurized up to 1500 psi or higher although many airless spray guns operate at lower fluid pressures, for example 900-1000 psi. An airless spray nozzle is therefore different from an air spray nozzle in order to effect a desired spray pattern and adequate atomization.
Airless spray guns sometimes produce an effect generally known as tailing in which the fluid near the outer region of the spray pattern is not atomized to the same extent as in the center region of the pattern. This effect can reduce the overall quality of the finished product. In order to eliminate tailing and to further improve the atomization process, an air assisted airless xe2x80x9cAAAxe2x80x9d hereinafter) spray process may be used. In such a process, although primary atomization occurs due to high pressure fluid passing through the nozzle orifice, atomization air may also be supplied and directed at the spray pattern in the region of the nozzle outlet.
Because each of the above described spraying processes utilizes different atomization and nozzle designs, it is not surprising that known spray guns usually only operate with a single spray process. Thus, there are airless spray guns, air spray guns, AAA guns and HVLP guns. For example, an airless spray gun does not have the hardware needed for air spray operation. An air spray gun typically will not operate as an airless gun. An air assisted airless gun will have air supplied to it, but typically will not operate satisfactorily as a true air spray gun.
Because these guns all use different spray technologies and nozzle designs, a spray gun manufacturer must keep a significant inventory of parts to build each gun type. Spray gun users may also need to keep a variety of spare parts to repair such guns.
Another spray technology is corona discharge electrostatic spraying in which an electrostatic charge is applied to the fluid as it is dispersed out the nozzle. The electrostatic charge helps to atomize the fluid, but more importantly is used to improve the transfer efficiency by utilizing the electrostatic attraction between the charged fluid and the object being sprayed. Electrostatic guns thus can utilize air spray technology such as air assisted and airless air assisted and HVLP. Accordingly, known electrostatic gun designs include the same problems of numerous parts, different gun designs for each technology and so forth as described hereinabove.
It is desired therefore to provide a new spray gun apparatus that can utilize a number of different fluid spray technologies using basic shared components that can be easily configured for a specific application.
To the accomplishment of the foregoing objectives, and in accordance with one embodiment of the invention, a significantly different approach is taken for designing a fluid spray gun by providing a spray gun that is modular so that the spray gun can be configured and built to operate using a selectable spray process. In one embodiment, a modular spray gun includes a gun body, an extension and a selectable atomizing component. The basic gun body and extension are used to configure a spray gun that can operate as an air spray gun, an airless spray gun, an AAA gun or an HVLP spray gun as well as an electrostatic spray gun using air, airless, air assisted or HVLP technologies. The modular extension can be selected to allow circulating or non-circulating operation. The modular extension also permits a variety of atomizing components to be mounted thereon depending on the selected spray process to be used with the specific gun. In an electrostatic version, the modular extension may house the high voltage multiplier.
The modular gun body allows selective connection of an atomizing air supply and additional components for air management specific to a particular spray process. In one embodiment the modular gun body and air management components allow separate air adjustment control for horn air and atomizing air depending on the selected spray technology.
In accordance with another aspect of the invention, an indicator device is provided for spray guns using an HVLP spray process to provide an indication that the spray gun is in compliance with the maximum nozzle air pressure limit of less than 10 psi.
In accordance with yet another aspect of the invention, a new air valve design is provided that can be used with the modular air spray guns described herein or with other devices that use air valves.
Still another aspect of the invention provides an atomizing component that enhances the modular features of the present invention in that there is provided a fluid flow element having a nozzle orifice therein, with the element being made of a lightweight non-metallic material such as plastic, for example, and includes a hard insert that is placed in the orifice. In a preferred embodiment the insert is made of carbide and is press fit into the orifice. The carbide insert thus allows a modular gun to be configured as an airless spray gun or as an air assisted airless spray gun by selecting the appropriate fluid flow element within a modular atomizing component. In accordance with a further aspect of the invention, an atomizing component or device is provided with significantly improved atomization for HVLP and air spray configured guns.
In accordance with a further aspect of the invention, a fluid tip and air cap arrangement is provided that optimizes atomization using a conical tip contour and a small flat area at the nozzle orifice. In the preferred embodiment the cone half angle is thirty degrees.
In accordance with other aspects of the invention related to the electrostatic technologies, a modular extension is used that houses a high voltage multiplier having a multi-step weight distribution. This positions most of the multiplier weight over the handle to reduce operator fatigue. In accordance with another aspect of the invention, an atomizing component includes an electric circuit path for an electrode, either molded with a fluid tip in the case of a high pressure gun or molded into a needle valve in the case of a low pressure gun. This greatly enhances the modularity and ease of use of the gun for assembly, repair and maintenance. Still a further aspect of the electrostatic version is a dynamic electrostatic seal that isolates the high voltage charge material from ground at the gun body to prevent discharge. Still a further aspect of the invention provides for an air cooled heat sink for the high voltage multiplier.